1. Field of the Invention
The present invention relates to an electronically controlled motor-driven system and operating method for powering a liftgate of an automotive vehicle. Although such liftgates are typically used at the rearmost part of vehicles, the present method and system may be employed with liftgates or doors used at a variety of locations on the exterior of an automotive vehicle.
2. Disclosure Information
As first used, automotive liftgates were most often manually operated. A pair of gas-filled or spring-loaded struts provided the force required to maintain the liftgate in its uppermost position, as well as assisting the motorist in opening the liftgate. Motor driven liftgates are a relatively new addition to the automotive genre. A motor drive typically powers the liftgate to its uppermost, or fully opened, position. When the liftgate is fully opened, the drive is typically declutched, allowing the gate to be maintained at its uppermost position by means of gas-charged telescoping struts. If however, the liftgate must bear the weight of a significant accumulation of ice, or an accessory such as a bicycle rack, it may be possible in certain cases for the combined weight to overcome the capability of the gas-filled struts, thereby allowing the liftgate to close in an unintended manner.
Designers of power liftgates have looked at controlling various operating features of the liftgate, such as closing speed under power, and a system for accomplishing this purpose is disclosed in U.S. Pat. No. 6,901,704. The system of the '704 patent does not, however, monitor either the position or unintended movement of the liftgate when it is in its opened position. U.S. Pat. No. 6,719,356 discloses a liftgate operating system having a proximity sensor which is used to stop operation of the liftgate. The system of the '356 patent again, however, does not monitor the liftgate when it is in a fully opened position to assure that the liftgate does not move out of control in an unintended fashion.
A method and system according to the present invention functions to prevent unintended movement of a liftgate regardless of the condition or load capacity of the telescoping struts normally assigned the task of maintaining the liftgate in an opened position.